The effect of two sources of magnesium fertilization (56 kg/ha, MgO). ensom salt and dolomite. on total alvcoalkaloid (TGA) and nitrate-nitrogen (N03-N) content of Katahdin potatoes was examined. Both magnesium fertilizers increased the TGA and NOJ-N content of tubers. Tubers grown in soils receiving epsom salt had significantly (p < 0.05) higher TGA content than the tubers receiving dolomite immediately following harvest, but after 5 mo storage, no significant differences were observed between the two Mg sources. The NO3-N levels in tubers from plants receiving Mg fertilization were higher than the controls. Those receiving epsom salt were higher than those receiving dolomite. The N03-N levels decreased in all tubers after 5 mo storage. Cortex tissue was significantly (p < 0.05) higher in N03-N than the pith.